1. Field of the Invention
This invention relates to an earth retaining system, and more particularly to a sheet pile retaining system having integral soil anchors.
2. Description of the Related Art
Marine related bulkheads constructed along the coast of Alaska experience some of the most severe environmental conditions known, including high waves and wave scour, earthquakes, ice, high tide variations, high phreatic water levels, weak soils, heavy live loads and difficult construction conditions. The need for low-cost, high load capacity docks and structures has resulted in a development of various sheet pile retaining structures.
Flat steel sheet piles have been used in perhaps the most simple form of structures featuring tension or membrane action primarily. Foundation designs of cellular cofferdams are discussed in detail in the text by Joseph E. Bowles, Foundation Analysis and Design (1977) herein incorporated in its entirety by reference. One configuration, a closed cell flat sheet pile structure, had been successfully used for many years for a wide variety of structures including cofferdams and docks. As shown in FIG. 1A, the most common use for flat sheet piles has been in closed cellular bulkhead structures of various geometrical arrangements. FIG. 1B illustrates another configuration, a diaphragm cell structure. By closing the cell structure, the entire structure acted as a deadman anchor in the retaining system to provide additional retaining support. However, positive structural aspects of this closed cell structure type were often offset by high construction costs. Several factors have contributed to higher costs, including: multiple templates required for construction alignment; close tolerances; difficulty with driving through obstacles and holding tolerance; backfilling operations using buckets or conveyors; and difficulty compacting the backfill. Modification of the closed cell to an open cell configuration provided higher accessibility and tolerance, but at a significant increase in material costs to offset the reduced load capacity of the cell configuration.
Yet another sheet pile retaining form has been the tied back wall masterpile system with flat sheet piles acting as a curved tension face. Tieback anchors with deadmen are connected to the curved tension face to provide lateral retaining strength as shown in FIG. 1C. This configuration allowed a higher load to be retained with fewer sheet piles used as the anchors and the sheets work in concert to retain the earth load. Tied back sheet pile walls often require deep toe embedment for lateral strength and if that toe embedment is removed for any number of reasons, wall failure will result. This method further required excavation for placement of the soil anchors, or an expensive and time consuming drilling operation to install the soil anchors, at the appropriate depth to integrate them with the sheet pile wall. Additionally, tied back walls are at risk in environments where waves overtop the wall and result in scour. Scour undermines the base of the bulkhead and the needed toe support resulting in failure of the bulkhead.
The present invention overcomes the limitations of the prior art and provides additional benefits. Under one aspect of the invention, a soil retaining system combining flat sheet pile walls in an open cell configuration with soil anchors integral to the sheet pile provides an improved earth retaining system. In one embodiment of the invention, the integral soil anchors are angular interlock soil bearing surfaces which provide higher load resistance. Another aspect of the invention is a method of designing and installing a soil retaining system with an open sheet pile cell structure having integral soil anchors. The method includes, inter alia, calculating soil resistance by taking into account soil friction against the sheet pile in combination with the strength of the integral soil anchor, selecting sheet pile size and length based on these calculations; and installation of sheet pile to form a soil retaining system.